1. Field of the Invention
The present invention relates to a current voltage converter circuit. More particularly, the invention relates to a current voltage converter circuit for use in, for example, a laser output automatic control system (hereinafter, referred to as an automatic power control (APC) system) for stabilizing a laser output at a predetermined value.
2. Description of the Related Art
In general, in the field of optical transmission such as wavelength division multiplexing (WDM) or a compact disk (CD), a laser output is stabilized at a predetermined value by using an APC system. Conventionally, in the APC system of this type, a current voltage converter circuit comprising a photo diode, a resistor, and an operating amplifier is widely used to detect a laser output. Some of the current voltage converter circuits each comprise a plurality of resistors having their different resistance values, wherein one of the plurality of resistors is selected, thereby making it possible to absorb a distortion of the photo diode (for example, a distortion of a photo receiving sensitivity according to a system). However, in the case of this current voltage converter circuit, the number of resisters increases as the distortion of the photo diode becomes large. Thus, there has been a disadvantage that this converter circuit is unsuitable to integration and is likely to increase in cost.
In addition, there is proposed a current voltage converter circuit further comprising a current distributor which distributes a current (light current) from the photo diode (refer to, for example, Jpn. Pat. Appln. KOKAI Publication No. 10-256841). This publicly known example discloses a system of adjusting a light current in a range which meets an output voltage range of the current voltage converter circuit by means of the current distributor, followed by supplying the adjusted current to the voltage converter circuit composed of the operating amplifier and the resistor.
In the case of the-described publicly known example, however, the current distributor is composed of a current mirror circuit. Thus, there has been a problem that, although the number of resistors can be reduced, a current after distributed is weak in fluctuation of a power voltage and a temperature change.